No, its 100% definitely not a limited production run driven by a hard number - like the CSS was.
It is "limited" in that they will only make them for a certain period of time - from whenever they start work on orders (maybe August as all CS45's will be MY22 cars) and until the end of December.
That's the limit.
In theory every Golf ordered/built in that time period could be a CS45, its only another slot on the Golf production line.